I. Zeolites
Zeolites typically are considered to be crystalline, porous aluminosilicates. In the late 1950s, Milton and coworkers (U.S. Pat. Nos. 2,882,243 and 2,882,244) determined that uniformly porous, internally charged aluminosilicate crystals could be made analogous to molecular sieve zeolites found in nature. Synthetic aluminosilicate zeolite molecular sieves are now used in numerous, commercially important catalytic, adsorptive and ion-exchange applications. Aluminosilicate zeolites provide a unique combination of high surface area and uniform porosity that is dictated by the “framework” structure of the zeolite crystals coupled with the electrostatically charged sites induced by coordinated metal atoms, such as tetrahedrally coordinated Al+3. Many “active” charged sites are readily accessible to molecules of the proper size and geometry for adsorptive or catalytic interactions. Further, the charge-compensating cations are electrostatically, not covalently, bound to the aluminosilicate framework. As a result, such cations are generally base exchangeable for other cations with different inherent properties. This provides significant flexibility for modifying active sites whereby specific adsorbents and catalysts can be tailored for a particular utility.
While a relatively large number of aluminosilicate materials are theoretically possible (see, for example, “Zeolite Molecular Sieves,” Chapter 2, 1974, D. W. Breck), to date only a relatively small number (approximately 150) have been identified. While compositional nuances have been described in publications, such as U.S. Pat. Nos. 4,524,055, 4,603,040 and 4,606,899, totally new aluminosilicate framework structures are rarely discovered. As a result, various approaches have been taken to replace aluminum or silicon in zeolite syntheses ostensibly to (1) generate either new zeolite-like framework structures or (2) induce the formation of qualitatively different active sites than are available in analogous aluminosilicate-based materials. E. M. Flanigan and coworkers have prepared aluminophosphate-based molecular sieves. (J. Am. Chem. Soc., 104, p 1146 (1982); Proceedings of the 7th International Zeolite Conference, pp. 103-112, 1986). However, the site-inducing Al+3 is essentially neutralized by the P+5, imparting a zero net charge to the framework. Thus, while a new class of “molecular sieves” was created, they lack “active” charged sites.
Realizing this inherent deficiency, there is a new emphasis on synthesizing mixed aluminosilicate-metal oxide and mixed aluminophosphate-metal oxide framework systems. This has generated approximately 200 new compositions. All of these new compositions suffer either from the active-site-removing effect of incorporated P+5 or the site-diluting effect of incorporating an effectively neutral, tetrahedral +4 metal into an aluminosilicate framework. No significant utility has been demonstrated for any of these materials.
The most straightforward method for potentially generating new structures or qualitatively different sites than those induced by aluminum would be direct substitution of some charge-inducing species for aluminum in a zeolite-like structure. The most notably successful example of this approach appears to be substitutions using boron, in the case of ZSM-5 analogs, or iron. [See, for example, EPA 68,796 (1983), Taramasso et al., Proceedings of the 5th International Zeolite Conference, pp. 40-48 (1980); J. W. Ball et al., Proceedings of the 7th International Zeolite Conference, pp. 137-144 (1986); and U.S. Pat. No. 4,280,305 to Kouenhowen et al.] The substituting species is incorporated only at low amounts, which raises doubt concerning whether the species are occluded or framework incorporated.
U.S. Pat. No. 3,329,481 ostensibly describes a method for synthesizing charge-bearing (exchangeable) titaniumsilicates under conditions similar to aluminosilicate zeolite formation if the titanium was present as a “critical reagent” peroxo species. These materials were called “titanium zeolites.” No evidence, other than some questionable X-ray diffraction (XRD) patterns, was presented to support this conclusion. The conclusions stated in the '481 patent generally have been dismissed by the zeolite research community. [See, for example, D. W. Breck, Zeolite Molecular Sieves, p. 322 (1974); R. M. Barrer, Hydrothermal Chemistry of Zeolites, p. 293 (1982); G. Perego et al., Proceedings of 7th International Zeolite Conference, p. 129 (1986).] For all but one end member of this series of materials (designated TS materials), the XRD patterns presented indicate phases too dense to be molecular sieves.
Naturally occurring titanosilicates also are known. For example, a naturally occurring alkaline titanosilicate, identified as “Zorite,” was discovered in trace quantities on the Siberian Tundra in 1972. See, A. N. Mer'kov et. al, Zapiski Vses Mineralog. Obshch., pp. 54-62 (1973). The published XRD pattern was challenged and a proposed structure was later reported in an article entitled “The OD Structure of Zorite,” Sandomirskii et al., Sov. Phys. Crystallogr. 24 (6), November-December 1979, pp. 686-693.
In 1983, trace levels of tetrahedral Ti(IV) were reported in a ZSM-5 analog. M. Taramasso et al.; U.S. Pat. No. 4,410,501 (1983); G. Perego et al., Proceedings of the 7th International Zeolite Conference, p. 129 (1986). More recently, mixed aluminosilicate-titanium(IV) structures have been reported [EPA 179,876 (1985); EPA 181,884 (1985)] which, along with TAPO [EPA 121,232 (1985)], appear to have no possibility of active titanium sites, and hence likely no utility.
II. U.S. Pat. Nos. 4,853,202, 4,938,939, and 5,989,316
U.S. Pat. No. 4,853,202, entitled “Large-Pored Crystalline Titanium Molecular Sieve Zeolites,” and U.S. Pat. No. 4,938,939, entitled “Preparation of Small-pored Crystalline Titanium Molecular Sieve Zeolites,” name Steve Kuznicki as inventor. Both the '202 patent and the '939 patent are incorporated herein by reference. The '202 patent discloses “ETS molecular sieve zeolites.” The '939 patent discloses a class of compounds referred to as ETS-4 having a pore size of from 3-5 Å. Table 1 below provides relative amounts of materials used to prepare ETS-4 as per Example 4 in the '939 patent.
TABLE 1Adsorbent ETS-4 (091504)ReagentAmountSodium Silicate25.1 gramsSodium Hydroxide 4.6 gramsKF 3.8 gramsTiCl316.3 gramsTemperature-Time150° C./170 hoursIon-Exchange10 grams ETS-4, 20 grams BaCl2,and 40 grams H2O @ 200° C.
According to the '202 patent and the '939 patent, which share significant common text:                These titanium silicates have a definite X-ray diffraction pattern unlike other molecular sieve zeolites and can be identified in terms of mole ratios of oxides as follows:1.0±0.25 M2/nO:TiO2:ySiO2:zH2O         wherein M is at least one cation having a valence of n, y is from 1.0 to 10.0, and z is from 0 to 100. In a preferred embodiment, M is a mixture of alkali metal cations, particularly sodium and potassium, and y is at least 2.5 and ranges up to about 5.The '939 patent, column 2, lines 39-50. Moreover, according to the '939 patent:        It should be understood that this X-ray diffraction pattern is characteristic of all the species of ETS-4 compositions. Ion exchange of the sodium ion and potassium ions with cations reveals substantially the same pattern with some minor shifts in interplanar spacing and variation in relative intensity. Other minor variations can occur depending on the silicon to titanium ratio of the particular sample, as well as if it had been subjected to thermal treatment. Various cation exchanged forms of ETS-4 have been prepared and their X-ray powder diffraction patterns contain the most significant lines set forth in Table 1.The '939 patent, column 4, lines 32-45.        Regardless of the synthesized form of the titanium silicate the spatial arrangement of atoms which form the basic crystal lattices remain essentially unchanged by the replacement or sodium or other alkali metal or by the presence in the initial reaction mixture of metals in addition to sodium, as determined by an X-ray powder diffraction pattern of the resulting titanium silicate. The X-ray diffraction patterns of such products are essentially the same as those set forth in Table T above.The '939 patent, column 6, lines 4-12.        
U.S. Pat. No. 5,989,316, entitled “Separation of nitrogen from mixtures thereof with methane utilizing barium exchanged ETS-4” discloses barium-exchanged compositions of ETS-4 which show particular utility in gas separation processes involving the separation of nitrogen from a mixture of the same with methane. The barium cation exchange can make the resulting composition more stable to heating. Heating to elevated temperatures is often required to activate the composition for use in adsorption applications.
Depending on synthesis conditions, these and other crystalline titanium molecular sieve zeolites of the prior art may have comprised fluorine plus possibly other halides prior to ion exchanging the M cations. However, no measurable (significant) halide content remains after the ion exchanging.